From University of Texas at Houston–Memorial Center for Healthcare Quality and Safety, Houston, Texas, and University of Utah School of Medicine, Salt Lake City, Utah.

Disclosures: Dr. Thomas helped to develop a commonly used safety culture survey and conducts research on safety culture. Dr. Classen is employed by a federally certified patient safety organization, which advises health care organizations about measuring and improving patient safety. Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M13-2528.

Recent studies in the United States and Europe suggest that despite some success at individual hospitals and reduced harm for 2 conditions (1), patient safety is not improving (2, 3) and remains a major public health problem (4). We have studied patient safety for 20 years, and these findings prompted one of us (Dr. Thomas) to review the case summaries of the 265 preventable deaths from the Utah and Colorado Medical Practice Study (5). The Institute of Medicine used these cases to estimate the number of preventable deaths due to medical errors for its landmark report, “To Err is Human” (6). In reading these summaries, one is quickly struck by the heterogeneity of the errors. Although the errors were broadly classified in our work as operative, drug-related, and diagnostic, these categories obscure the diverse nature of the errors and adverse events. For example, the most common category (operative) contained 20 types of adverse events, each of which comprised additional subtypes and were caused by a large variety of errors (7).